Help! Electrical Trouble on 500SEL (1985)
 

Long story but here goes...I was replacing a light bulb in the climate control unit and accidently shorted it to ground just for a second (do not ask me how). I put everything back together and I had no dash lights at all, the fuel gauge pegs and the temp guage pegs when you turn the lights on. They also jump when you turn the brights on. When I buckle the seat belt, the seat belt and bright lights warnings come on very dim.
I pulled the guage cluster and it smelled like something burned. I replaced the guage cluster (Left side) with the dimmer control and now I have dash lights but everything else is still happening. Did I burn some wireds together or is there an other suggestion?
Any help would be appreciated!
THANKS!

There are a couple possibilities. One is that you burned the ground lead somewhere in the printed circuit. This is usually pretty evident if you open it up and examine the ground trace.

Another possibility is that in disassembling the cluster you haven't re-established the link across the various units. They are connected by contact as they are screwed together. I have seen a number of cases where just retightening the screws on the back will make the connection.

Steve:
Does the 126 chassis have that printed circuit fuse in the back of the cluster like a 300E, the one that looks like a red base light bulb, but no bulb, just the printed circuit chip in it?
Gilly

W140 '92 300SD gages gone haywire
 

Hello,

Seems I have similar problem. But first, what is an ETM? What does the ETM acronym stand for?

I have a '92 300SD which goes haywire when I use the turn signals. This first started happening when I drove the car during a rainy evening. Almost everytime when I use the turn signals (or emergency blinker), the instrument cluster gage needles seem to get "shocked!" Seems as if the instruments reset because several gage needles jump / peg to a zero position and diagnostic indicator lights flash. The gage needles in question are:

1. oil pressure gage needle (and red light)
2. coolant temperature gage needle
3. fuel economy gage needle
4. safety belt light blinks (most consistent)
5. low oil level indicator lights up and turns off
6. battery indicator lights up and turns off
7. "exterior light bulb out" indicator
8. other indicators flash on and turn off.

All this happens at once only during the first 'blink' of the turn signal. If I keep the turn signal on, the gages go back to showing what they're intended to measure. Sometimes, however, with the emergency blinkers on, the needles continually reset with every 'blink.'
This behavior consistently repeats while driving but happens much less (rarely) when the car's transmission lever is in parking position.

I am clueless as to what might be the cause for such erratic behavior. I am 99.9% sure that it isn't caused by water, because I live in Phoenix, Arizona, and it has been at least 4 months since this first started happening. During this time, I've not driven the car in rainy weather at all.

I will very much appreciate any advice on how to diagnose and repair this problem.

Many thanks,

Branimir


'92 300SD (119K mi)
'82 300SD (295K mi)
'81 240D (126K mi)

ETM is the Electrical Troubleshooting Manual, it is just MB's fancy name for wiring diagrams.
It sounds like your problem may be from a bad instrument cluster ground.
Gilly

There is probably a blown fuse somewhere. Weird symptoms like this show up when a ground is missing. I have also seen symptoms like this when power is supplied to a circuit through the ground side as a result of blown fuses in another circuit(GM cars).